The present invention relates to a low noise oscillator operating in the ultra-high frequency range, and organised around a plurality of transistors stabilized by a single dielectric resonator.
The invention relates to the field in which transistors operate in conjunction with microstrips and dielectric resonators. It is applicable to relatively low frequencies, such as 1 or 2 GHz, with bipolar transistors. However, it is of particular interest in connection with field effect transistors and at higher frequencies, such as e.g. 11 to 14 GHz.
The use of dielectric resonators, i.e. pellets of high value dielectric material, for stabilizing transistorized oscillators is well known, as is the interest in such a stabilization. Such devices permit thermal stability levels controlled by the choice of the characteristics of the resonator material, and the noise characteristics close to the carrier wave and particularly low, due to the low dielectric losses of the materials used for this purpose. This type of oscillator stabilization makes it possible to obtain a pure frequency by direct generation, without using a frequency multiplier chain.
However, in certain applications, it is necessary to have a source which, at the considered frequency, has a power higher than the power made available by a single transistor. For the same applications, it is often necessary for the power to be very stable and for the oscillator only to have a low background noise around the generated frequency.
A first known solution consists of the parallel connection of a plurality of oscillators, each having at least one transistor and a stabilizer by dielectric resonator. However, in this case it is virtually impossible to obtain resonators having in each case the same noise level and which are all identically coupled with the oscillator. This is a reason why a circuit making it possible to couple several oscillators to the same resonator is of interest, because it makes it possible to couple the transmitted power without adding the noise. However, even though the power level is not the main objective sought, the increase in the number of active elements coupled to the same resonator is of interest in connection with the noise of the oscillator close to the carrier. The first reason is linked with an increase in the coefficient Q.sub.ext, which is the ratio between the energy stored in cycles in the resonator and the power supplied to the load. With a given output power, it is possible to couple more energy in the single resonator. A second reason is that the ultra-high frequency signals from the different transistors are summated in phase, whereas the noise levels are summated in an uncorrelated manner, i.e. the signal-to-noise ratio of the device improves.